1. Field of the Invention
The present invention relates to the field of automotive design, manufacture and assembly, and more particularly to an automobile chassis and body which are highly resistant to head-on, broadside and rear-end collisions, have low fixed and recurring production costs, are manufactured using processes minimizing waste products and eliminating toxic vapor emissions, and are almost totally comprised of recyclable materials. Specifically, a chassis comprised substantially of aluminum alloy and thermoplastic and a body and interior panels consisting entirely of thermoplastic provide stronger, lighter and cheaper alternatives to reinforced steel frames and sheet-metal body panels currently utilized universally by automobile manufacturers.
In order to build cars comprised of thousands of parts, current automotive construction systems require massive investment in plant and equipment, are energy and labor intensive, are major contributors to pollution, and produce end-product vehicles that often vary substantially in quality. In marked contrast, constructing an automobile in accordance with the principles of the invention enables substantial reduction of the types of materials and numbers of parts needed and makes parts much easier to assemble and disassemble, thus minimizing the labor and energy required, while enabling superior quality control during production, and ensuring that materials eventually recycled can be efficiently restored to high manufacturing quality.
2. Description of the Related Art
Many global, regional and national problems result directly from how automobiles currently are designed, manufactured, operated over their useful life, and eventually discarded. These problems include significant depletion of natural and industrial resources, widespread pollution of air, land, and water by the enormous industrial infrastructure required for fabricating and assembling parts and for disposing of manufacturing waste and automobile scrap, poisoning of the atmosphere by engine exhaust emissions and by toxic vapors released during conventional manufacturing processes, and the large numbers of people killed or injured in automobile collisions.
Responding to changes in consumer preferences, governmental legislation and the pressures of global competition, automobiles have become smaller, lighter and more energy efficient. In 1977, 51 percent of all automobiles on U.S. roads were large; by 1990, large autos totaled 39 percent. In 1972, average curb weight was 4500 lbs.; by 1990, average weight had decreased to 3200 lbs. In 1973, many U.S. made cars had 400-plus horsepower engines providing only 6-8 mpg; by 1993, average mileage was 28 mpg. Presently, one-third of the automobiles sold in the U.S. are compact- or subcompact-sized.
Despite these trends, automobiles have become increasingly expensive, leading people to keep aging cars longer. In 1971, the percentage of automobiles scrapped compared to those in service was 9 percent; by 1991, they were 6.5 percent. In 1980, 12 percent of passenger cars in the U.S. were at least 12 years old. In 1990, the percentage had nearly doubled to 21 percent.
Exhaust emissions from the increasing numbers of older automobiles kept operational have frustrated efforts to reduce air pollution by improving engines and installing catalytic converters. Particularly in California, where benign weather and salt-free roads greatly extend the life of cars, there is an abundance of pre-emission control vehicles that spew out exhaust emissions at rates up to 100 times greater than that of new cars.
Large-scale conversion to zero-emission vehicles, particularly battery powered electric cars, has been proposed as a panacea for reducing air pollution. However, such cars are expected to have sticker prices $5,000 to $10,000 higher than those of conventional cars of similar size having superior performance. Moreover, there necessarily will be significant increases in power plant emissions resulting from charging large numbers of electric vehicles. Thus, in areas where power plants are fueled by coal and oil, the energy demands of electric cars may on balance worsen air quality.
Despite innovations in automobile design contributing to occupant safety such as seatbelts, crumple zones and air bags, and despite the U.S. being the second safest driving country, tens of thousands of people have been killed in traffic accidents over the last three decades and millions more have been injured. Many of these fatalities and injuries result from inability of conventionally designed and built chassis and bodies to withstand high-load impacts and resultant stresses.
Today, a typical mid-size car built in the U.S. consumes about 1200 lbs. of low-carbon steel, 230 lbs. of high-strength steel, 80 lbs. of stainless and other steels, 400 lbs. of iron, 160 lbs. of aluminum, 130 lbs. of rubber, 220 lbs. of plastic, 80 lbs. of glass, 50 lbs. of copper, 20 lbs. of zinc, 25 lbs. of powder metal, and 170 lbs. of fluids and lubricants. In total, the U.S. automotive industry uses over 23 million tons of materials annually, including about two-thirds of the iron, one-fifth of the steel, half of the rubber, and one-fifth of the aluminum produced domestically.
At the end of its operational life, an automobile typically is composed of relatively low value materials, primarily low-carbon steel, iron, aluminum and low grade plastics. More than 9 million automobiles are scrapped each year. Of these, over 90 percent are recycled through an established infrastructure which includes about 12,000 dismantlers and 200 shredding facilities producing 50,000 metric tons of residue annually. Approximately 75-80 percent of the weight of an average automobile is recycled, including most of the steel, iron and aluminum. Battery plates, housings and sulfuric acid are reprocessed; oil, coolants, and refrigerants are reclaimed. Waste textiles are shredded to produce sound insulation, while thermoplastic remnants from production lines, mixed with reclaimed scrap material, are melted down and used to form trunk linings, spare tire covers and ventilation ducts. The average car's plastic content has more than doubled since 1972. Plastic bumper covers, interior panels, trim moldings, bumper beams, fuel tanks, valve covers and oil pans are all in common use today. Although steel and aluminum require much greater amounts of energy to recycle than do plastics, more than one million tons of plastic components from scrapped automobiles end up in landfills each year because it presently is not cost-effective to recover and recycle plastic.
The issue in automobile recycling is not intrinsic feasibility but cost-effectiveness which depends on how easily separable parts are, how many and what types of materials must be separated, and the value of recycled materials. Due to the current trend of increasing complexity in automotive design, it is likely that cars will become more expensive to recycle than they are now because their disassembly and reprocessing will become increasingly complex.
In recent years, composite materials including high performance thermoplastics have been successfully applied to racing car chassis, replacing riveted steel and aluminum sheets. Engineering advantages of composites include increased torsional and bending stiffness, improved crash-worthiness, ease of repair and reuse, and structural stability over time. Studies by the Ford Material Research Laboratory have shown that composites can absorb nearly twice the energy-per-unit weight than can steel. Also, stable molds enable reproducible dimensional accuracies during chassis production runs. Tooling cost comparisons show molding equipment to be significantly cheaper than steel presses needed to fabricate sheet-metal panels.
High performance thermoplastics can readily be fabricated into molded products, and can be conveniently melted down for reuse provided that different types are not mixed. They offer high strength-to-weight capabilities, rigidity and toughness, superior thermal and hydrolytic stability, excellent flammability resistance coupled with low smoke generation, and low permeability to moisture and organic solvents. Thermoplastics are particularly well suited to the automotive industry as they can withstand attack by acids, bases, hydrocarbons, gasoline, gasohol, oxidizing solutions, and many other chemicals and solvents.
Among high performance thermoplastics, polycarbonates and liquid crystal polymers (LCP) exhibit some of the highest tensile and flexural performance. In their toughest forms, these thermoplastics are highly wear resistant, and have superior tensile strength and superior flexural modulus.
Lightweight thermoplastic foam sandwich panels have not heretofore been used in the automotive industry. They have, however, been successfully used to construct transportable airfield surfaces which support rapid deployment fighter aircraft. Such surfaces can withstand well over a hundred take-offs and landings.
Sandwich structures including composite materials have been used in constructing light-weight, high efficiency helicopters. Compared to conventional helicopters, payload at equal power is increased due to a lighter structure. Such structures are more expensive than conventional structures containing low cost materials, but enable using automated manufacturing procedures which provide a net economic gain of approximately 30-50 percent. Use of composite sandwiches also enables greater reliability and ease of maintenance, substantially reducing mean time to failure and risk of malfunction.
Fiber-reinforced thermoplastics have been used in thermoplastic/aluminum sandwiches, together with aluminum foam, to construct helicopter chassis and fighter aircraft wing sections. Such thermoplastics have also been used in missile nose cones and artillery shell casings.
Injection molding in-situ where light-weight steel structures are used as frame members is known in the plastics rotomolding art. Also, use of honeycomb prefabricated in flat sections is known in the structural fabrication arts. However, use within a larger structure of thin-wall three-dimensional aluminum honeycomb substructures which serve as molds for injecting unreinforced or reinforced thermoplastic foam has been heretofore unknown in the thermoplastic molding and composite structural fabrication arts.
The racing car industry has made use of monocoque body design, a light, rigid type of construction in which the body is integral to the chassis and the outer skin serves as the frame in that it carries most or all of the stresses. Aluminum and steel are the most common materials used for monocoque chassis.
An all-plastic monocoque tub chassis, developed by Chaparral Cars in 1964, was substantially lighter and stiffer than the steel-tube racing frames then in use. The chassis tubs weighed 120 to 140 lbs. and had 3,000 to 3,500 lb-ft/deg torsional stiffness. The design included two long torque boxes, or pontoons, disposed on opposite sides of a cockpit and engine bay, the forward halves of the pontoons serving as fuel tanks. The pontoons were connected at the front by a box-shaped footwell, by a shallow third fuel tank extending the width of the cockpit and disposed under the driver's knees, and by an integral seatback structure. All of these components were fabricated from plastics incorporating glass fiber, including glass fiber honeycomb. None was directly subject to point loads.
A conventional automobile chassis frame constructed of steel or aluminum members typically requires angled cross-pieces between orthogonal members to withstand point-load stresses imposed on the frame. However, use within a chassis frame of honeycomb substructures incorporating unreinforced or reinforced thermoplastic foam which serve to withstand compressive stresses imposed by point-loads on the frame by diverting and diffusing such loads throughout the chassis interior is heretofore unknown in the automotive design arts.
It is unlikely that the enormous resource conservation, environmental, industrial, economic and safety problems created and perpetuated by the automotive industry can be significantly ameliorated by token or piecemeal improvements in how cars are designed, built and scrapped. Dealing effectively with these national, and indeed global, problems will require a radically new and integrated approach to how motor vehicles are designed, manufactured, assembled, operated and reclaimed.